Initial stages in the growth and development of junctions in heteroepitaxy of InP on GaAs

The initial stages in the growth of indium phosphide films on gallium arsenide substrates in a chloride gastransport system are investigated by transmission electron microscopy and electron-diffraction and secondaryion mass spectrometry techniques. It is shown that decomposition and/or etching of the surface oxide film and formation of a chemically pure substrate surface occur in the initial stage of the process. The growth islets that form on this surface constitute a solid solution in InP. A model of the process is proposed. V. D. Kuznetsov Siberian Physicotechnical Institute at Tomsk University. GNPP “NIIPP”. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 85–90, June, 1996.     

Refined “statistical” model of secondary ion formation

A model of formation of secondary ion during ion-beam sputtering of a target is considered. The model is based on the so-called “statistical model” of formation of secondary ions at a certain critical distance from the surface, which was proposed earlier. The concept of dynamic temperature introduced in earlier publications for a cascade of collisions initiated by a primary ion, as well as a new interpretation of the interaction of the formed ion with the surface charge of opposite polarity, enabled us to derive an analytic expression for the ion formation probability. Comparison of the results of calculation with experimental data shows good agreement testifying the correctness of the proposed model.     

Structural ordering and self-organization effects in multilayer Pd/Fe films

The structural features of the distribution of Pd and Fe atoms in multilayer films derived via Penning-discharge sputtering are studied. The preparation of films is a highly nonequilibrium process; at the same time, it is relatively simple in terms of possible structural implementations, which are shown during the self-organization of sputtered atoms through the formation of clusters with an individual ordered structure. It is important that the “dynamic chaos” that appears during sputtering is stabilized during crystallization, which makes it possible to study the resulting structures using nondestructive inspection methods with fairly wide possibilities. Therefore, it is of interest to study self-organization during the sputtering of multilayer films in order to reveal the mechanisms of cluster formation and to simulate them. It is also shown that the self-organization during sputtering and subsequent crystallization is accompanied not only by the ordering in the form of clusters, buts also by an ordered arrangement of these clusters.     

Properties of indium phosphite and selected compounds under irradiation with swift heavy ions

Surface and bulk properties of indium phosphate single crystals with initial and previously irradiated by 25 MeV electrons structures were irradiated with ⁸⁶Kr (253 MeV) and ¹⁹⁷Au (200 MeV) up to various fluences. The modern methods of condensed matter studies were used for research of InP property changes before and after irradiation as scanning (SEM) and high resolution transmission electronic microscopy (HTEM), Rutherford backscattering spectroscopy (RBS/C) and atomic force microscopy (AFM). The comparison of obtained results with the results of other authors is carried out. The surface structure change of InP single crystal irradiated by high-energy 86Kr ions and electrons is studied. It is shown the changes of the InP surface have complicated character and caused by inelastic sputtering processes. It is observed the twice irradiated layer swells with the cracks creation on the surface. The swelling with cracks and strong sputtering of twice irradiated by electrons and ions with high energy layers of the InP and GaAs surfaces are explained using the model based on the influence of ionizing energy loss of swift ⁸⁶Kr ions. The small crystalline objects are detected on the InP surface irradiated with ⁸⁶Kr ions which may be nano- and micro-crystals of InP. All obtained effects are discussed in frame of models based on ionizing energy loss of swift heavy ions.     

一种可能的InP(100)(4×2)表面原子结构模型

对于用氩离子刻蚀并在磷气氛中退火得到的InP(100)(4×2)再构表面,用HREELS测得表面的In—H和P—H键几乎是同时形成的,而用偏振光UPS观察时,P的悬挂键电子态并不具有沿原胞两个周期方向的对称性质。根据这些结果,可以推测InP(100)的富In表面存在In的空位,与In空位相邻的P原子悬挂键发生了转向。我们提出了一种失列-二聚物原子结构模型。它可以定性地解释所观察到的实验事实。 关键词：     

SEM and XPS studies of nanohole arrays on InP(1 0 0) surfaces created by coupling AAO templates and low energy Ar ion sputtering

The aim of the present study is to demonstrate the feasibility to form well-ordered nanoholes on InP(1 0 0) surfaces by low Ar⁺ ion sputtering process in UHV conditions from anodized aluminum oxide (AAO) templates. This process is a promising approach in creating ordered arrays of surface nanostructures with controllable size and morphology. To follow the Ar⁺ ion sputtering effects on the AAO/InP surfaces, X-ray photoelectron spectroscopy (XPS) was used to determine the different surface species. In_4d and P_2p core level spectra were recorded on different InP(1 0 0) surfaces after ions bombardment. XPS results showed the presence of metallic indium on both smooth InP(1 0 0) and AAO/InP(1 0 0) surfaces. Finally, we showed that this experiment led to the formation of metallic In dropplets about 10 nm in diameter on nanoholes patterned InP surface while the as-received InP(1 0 0) surface generated metallic In about 60 nm in diameter.     

Deformation enhanced photoemission from aluminum

Measurement of the photoyield of flexurally fatigued aluminum is reported as a function of photon energy for two different initial microstructures of the material. It was found that for photon energies less than about 9 eV fatigue enhances the photoemission. It was also observed that this “photo-stimulated exoelectron emission” is quite sensitive to the initial microstructure. The enhancement occurs much more rapidly with fatigue for well-annealed Al than for work hardened specimens. The results appear to be consistent with a model, to be presented in Part II which is based on a resonant coupling between the surface electromagnetic modes (plasmons) of the metal and the incident photon. This resonance is made possible by the development of dislocation slip steps on the surface during fatigue. The effect of material condition is shown to be primarily a difference in the kinetics of slip step formation. The effects of ion sputtering to remove oxides and of the angle of incidence of the photons are also reported. Above 9 eV the photoyield was found to be almost insensitive to fatigue, usually decreasing slightly.     

提高InGaAsP/InP DH面发光管输出光功率的研究

用改进了的射频溅射仪,对InGaAsP/InPDH面发光管窗口沉积Al2O3抗反射层,以提高光功率的输出。本文采用了两种涂层途径,其一是对单个发光管窗口直接涂层,另一则是对发光管管芯片上窗口涂层,并对二者作了比较。     

Direct evidence for In-crystallite growth on sputter-induced InP cones

High-resolution transmission electron microscopy proved that the cone evolution on Ar⁺-sputtered InP(100) entails the growth of In crystallites on the cone surface, obviously due to a preferential loss of P atoms. The In crystallites grew on the cone shank, as well as the cone tip, in a definite orientation formulated as InP(011) ∥ In(010) with InP[001] ∥ In[101̄]. The cones themselves were solely composed of InP, but involved the polycrystalline phase surrounding the original monocrystalline phase. Such a structural duality of InP cones may indicate that the target surface was in a quasi-liquid state during sputtering.     

Sputtering of A 3 B 5 materials (GaP, GaAs, GaSb, InP, and InSb) by 2-to 14-keV N 2 + ions

Investigations of the general characteristics and distinctive features of sputtering of A ³ B ⁵ materials (GaP, GaAs, GaSb, InP and InSb) under bombardment with N ₂ ⁺ ions have been carried out. From the experimental data, dependences of the sputtering yield of these materials on the incidence angle and ion energy have been obtained and the surface relief patterns produced by target etching have been studied. It has been shown that the dependence on energy of the sputtering yield for GaP, GaAs, and InP can be adequately described by the Haffa-Switkovski formula for binary materials and Yudin’s approximation for elemental targets. Sputtering of GaSb and InSb proceeds in the surface layer recrystallization mode, and the sputtering yield agrees with calculations based on Onderlinden’s model. From a comparison of the experimental and calculated dependences, the surface bonding energies have been determined.     

On the problem of nucleation (cell formation) in self-organization of protein nanostructures <Emphasis Type="Italic">in vitro</Emphasis> and <Emphasis Type="Italic">in vivo</Emphasis>

No convincing theory or hypothesis concerning the origin of biological cells exists today. Insight into the problem is difficult, because an empiric model of cell origination and division at the crucial phase of life, self-organization of protein nanostructures, is lacking. It has been shown experimentally that protein nanostructures exhibit signs of self-organization when an open far-from-equilibrium protein-water system condenses in vitro. In other words, to be active, protein must be in the nonequilibrium state. Such a form of self-organization is accompanied by nucleation and the formation of defects, which divide the protein film into domains (“cells”) with nuclei. This type of structuring in the nonequilibrium (active) protein may be viewed as a crude empiric model of protein nucleation, since it includes the formation and division (self-organization) of biological cells, the origination of which, in turn, is intimately related to the self-organization of protein at the nanolevel. The reason for the similarity of the basic processes is identical conditions of protein condensation in vitro and in vivo. In both cases, when water evaporates rapidly from an open water-protein system that is far from thermodynamic equilibrium, the conditions necessary for protein nonequilibrium nanostructures be self-organized with nucleation in the form of nucleus-containing “cells” are set.     

Ajellium model analysis on quantum growth of metal nanowiresand nanomesas

A simple jellium model is used to investigate the stability of a metal nanowire as a function of its size. The theoretical results from the model indicate the quantum selectivity of preferable radii of nanowires, in apparent agreement with the experimental observations. It is consequently suggested that a series of stable “magic numbers” and “instability gaps” observed in the synthesis experiments of Au nanowires is mainly attributed to the quantum-mechanical behavior. These stable radii can be achieved by rearranging atoms during the formation of nanowires. The model is also used to analyze the growth of Au nanomesas on a graphite surface, and the puzzling growth behavior of Au nanomesas can be reasonably explained.      

On the direct observation of the gas-dynamics of laser-pulse sputtering of polymers

We bring together a wide range of ideas relating to the gas-dynamic effects that are now recognized to play a leading role in laser-pulse sputtering. The ideas are grouped according to three basic models. (a) In the effusion model one deals with particles which are released from a target surface, form a Knudsen layer (KL), and then enter an unsteady adiabatic expansion (UAE). When the release terminates at time t=_r there is an abrupt change at the surface from positive to zero flow velocity, which means that particles moving towards the surface are reflected. The flow breaks up into three regions and analytical solutions exist for all aspects of this flow. (b) In the recondensation model the comportment of the target is initially like that of the effusion model but when the release terminates at t=_r the change at the surface is from positive to negative flow velocity, meaning that particles which move towards the surface recondense. Only numerical solutions presently exist (due to Sibold and Urbassek) but they are sufficient to show that the flow breaks up into two (not three) regions. (c) The outflow model could be described as the escape of gas from a finite reservoir, a well-known problem since it describes some aspects of guns. In its application to laser sputtering it is assumed that bond-breakage occurs rapidly over a characteristic depth and the resulting gas-like particles then flow out in a UAE; there is no formal KL.For part II, in which explicit photographs of laser-sputtered particles are analyzed, see [1]     

Formation of nanodots on oblique ion sputtered InP surfaces

Using a field emission gun based scanning electron microscopy, we report the formation of nanodots on the InP surfaces after bombardment by 100 keV Ar⁺ ions under off-normal ion incidence (30° and 60° with respect to the surface normal) condition in the fluence range of 1 × 10¹⁶ to 1 × 10¹⁸ ions cm⁻². Nanodots start forming after a threshold fluence of about 1 × 10¹⁷ ions cm⁻². It is also seen that although the average dot diameter increases with fluence the average number of dots decreases with increasing fluence. Formation of such nanostructured features is attributed due to ion-beam sputtering. X-ray photoelectron spectroscopy analysis of the ion sputtered surface clearly shows In enrichment of the sputtered InP surface. The observation of growth of nanodots on the Ar⁺-ion sputtered InP surface under the present experimental condition matches well with the recent simulation results based on an atomistic model of sputter erosion.     

Surface modifications of materials by repetitive laser pulses

Laser-induced modifications on platinum (Pt) and silicon (Si) are compared by considering the development of various features on the irradiated surface. The experiments were carried out both in air and under vacuum. The interaction of 50 pulses of 1064 nm Nd:YAG laser with both targets in air resulted in non-linear phenomena. The periphery of the irradiated spot on the Pt surface exhibits wave-like patterns with a featureless central portion. A non-uniform distribution of cones of different sizes is also observed on the irradiated surface. In the case of silicon, the laser-induced periodic surface structures along with the formation of micro-column, rectangular blocks and grid are prominently observed features. However, when both the targets were irradiated with the same number of shots under vacuum (～10^?3 Torr), the surface morphologies of both the targets exhibited the hydrodynamic sputtering but with more explosive expulsion in Pt when compared with silicon. In platinum, there is a periodic variation in the distance between adjacent cones formed in various ablated zones. The Gaussian beam mode TEM₀₀ provided the evidences for melt pool formation in silicon when irradiated under vacuum. Additionally, we observed other mechanisms including splashing, sputtering, burning, re-solidification and redeposition on the surface of irradiated targets.     

Sputtering of compound semiconductor surfaces. II. Compositional changes and radiation-induced topography and damage

Ion bombardment often leads to compositional changes in the surface layers of multicomponent targets. Such changes due to noble gas ion sputtering are discussed for InP and GaAs. The analyses show that the compositional change in InP (i.e., indium enrichment) is mainly due to preferential sputtering. In the case of GaAs. the changes are due to radiation-induced diffusion and segregation effects. Brief mention is made of compositional changes in a few other systems. The discussion on sputter-induced topography development deals mainly with InP because ion bombardment leads to dramatic topographical effects in this material. Ripple development on GaAs is also briefly discussed. Radiation damage has been well researched, and its mechanism and effects usually differ substantially when going from one semiconductor group to another. Bombardment-induced damage is briefly discussed for InP, GaAs, SiC, some II-VI semiconductors, and HgCdTe.     

Degradation of gallium arsenide under irradiation with an excimer laser

The results of a study of degradation of the surface of gallium arsenide resulting from irradiation with a power excimer laser at power densities ranging from the threshold power to the power level causing local melting of the surface are presented. Two degradation mechanisms have been identified, one of which causes the formation of a thin near-surface layer of modified nonstoichimetric gallium arsenide at a power level higher than 1×10⁷ W/cm² and the other of which causes the formation of a separate gallium phase. The formation of the separate gallium phase can be produced either by a single pulse of laser radiation with a power density exceeding 2.7×10¹¹ W/cm² or by a few less powerful pulses. An empirical relationship has been established between the power density and the number of pulses causing the formation of the separate gallium phase. It has also been established that as a result of laser irradiation at the boundary of “cold” and “hot” gallium arsenide, periodically ordered defects in the form of blocks aligned along the [100] directions emerge.     

Ultraviolet photoelectron spectroscopy of nano In clusters Schottky barriers on sputtered InP

Plasmon peaks along with Auger P_LVV peak have been observed in the ultraviolet photoelectron spectra (UPSs) of InP after 5 min of sputtering with 0.5 kV Ar⁺ ions. Plasmon and Auger peaks are not observed in UPS of un-sputtered InP surface with native oxides of In and P. Filled electron energy levels are not observed near the Fermi level from 5 min sputtered InP surface due to increase of ionization potential of nano In clusters.     

Ion beam sputtering of multicomponent targets: Surface composition change and cluster emission

Preferential sputtering effect, which occurs during irradiation of a multicomponent target by medium energy ions, was under our investigation. A new term characterizing the preferential sputtering, called “surface sputtering yield” and defined as average number of components i sputtered from a top surface layer per one primary ion, was suggested. A direct proportionality between the dimer emission and surface concentration of the component, forming the dimer, was concluded; this let us estimate the preferential sputtering of any target from the composition of the flux of secondary particles, analyzed directly during the ion sputtering process, and define the composition of the ion sputtered surface.     

Optical conductivity in a simple model of a pseudogap state of a two-dimensional system

Calculations of the optical conductivity are performed in a simple model of the electronic spectrum of a two-dimensional system with “hot regions” on the Fermi surface. The model leads to a strong restructuring of the spectral density (pseudogap) in these regions. It is shown that this model makes it possible to reproduce qualitatively the basic features of the optical measurements in the pseudogap state of high-temperature superconducting cuprates. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 6, 447–452 (25 March 1999)